First attempts at harnessing water as a source of energy were through waterwheels used for grinding, pumping, and driving various types of equipment. Some accounts suggest waterwheels were first used as long as 4,000 years ago. These water wheels used either the elevation change across the wheel to turn it as in the case of an overshot waterwheel or used the velocity of the water to turn the wheel as in an undershot or vertically mounted waterwheel. The undershot and vertically mounted waterwheels were based on the principle of reaction forces, with the force of the water pushing buckets or paddles along causing the wheel to turn. Generally, this was a highly inefficient means of energy extraction.
In about 1931, the French inventor Georges Darrieus developed the concept of a vertical axis wind turbine using the principle of lift instead of reaction forces. However, the principle is essentially the same whether the turbine is used in wind or in water. In fact, the Darrieus-type wind turbines have been adapted to vertical-axis hydrokinetic turbines. The most significant difference is that the Darrieus-type vertical-axis hydrokinetic turbines utilize straight blades as opposed to an eggbeater design of the original Darrieus wind turbine. These Darrieus-type vertical-axis hydrokinetic turbines have a series of aerodynamically shaped blades that are mounted parallel to a vertical central shaft in a concentric arrangement. The individual hydrofoil-shaped blades are connected to the central shaft by support arms. The shaft transmits torque to a generator or other power transfer device. These hydrokinetic turbines can be supported by floating platforms anchored to the river bottom/sides or structures supported on the river bottom.
While these prior water turbines have been shown to be a potentially viable technology, commercially available water turbine systems have not been cost effective because they are expensive to manufacture and assemble and because they produce relatively small amounts of power due to their low efficiencies. Additionally, they are difficult to transport and install. Also, they are not particularly efficient in extracting energy and can create a significant impediment to a waterways flow. Accordingly, there is a need in the industry for an improved hydrokinetic water turbine system.